Shockproof receiver control



Jan. 2, -1951 c. F. HOFFMAN SHOCKPROOF RECEIVER CONTROL Filed Oct. 20, 1947 INVEN TOR.

/Ff'0/F0 F HOFFM/W Patented Jan. 2, 1951 SHOCKPROOF RECEIVER CONTROL Clifford F. Hoffman, Chicago, 111., assignor to Admirai Corporation, Chicago, 111., a corporation of Delaware Application October 20, 1947, Serial No. 786,903

(ill. 259-16) 5 Claims. I

This invention relates to improvements in controls for electrical apparatus, and more particularly to an improved control knob which is useful in connection with the controls of electrical apparatus including radio receivers, transmitters and the like.

In connection with radio receivers, it is customary to provide metal shafts which eXten through the front of the cabinet housing the re ceiver, and which shafts are provided with knobs to facilitate the operation thereof. The shafts usually connect to the receiver controls such as the volume control, which may be mounted on the receiver chassis, as well as to the station tuning controls.

in some types of receivers, there is substantially no danger of shock to the operator. This is particularly true of properly constructed alternating current operated receivers wherein the conventional transformer is used to provide the power supply. In the construction of receivers which will operate on alternating or direct current, however, it is necessary to take special precautions, otherwise the operator may obtain a shock if he comes into contact with the receiver chassis or bare controls and if he happens to be standing or is in contact with a ground. Since the control shafts usually extend through the front of the cabinet, it not infrequently happen that the knobs become loose and fall off, and although they should be replaced, they may not be. In some instances during the act of replacing the same, the operator is apt to engage the shaft with his bare hands.

As a result of the foregoing, it has been customary, in conventional A. C.D. C. broadcast receivers, to reduce the probability of shock by providing a circuit ground which is independent of the chassis. Even in this case, accidental grounds are liable to occur which increases the possibility of shock. This construction is such as enables the radio manufacturer to obtain the aproval of the Underwriters Laboratories, Inc.

Although the separate ground affords a satisfactory operation of the radio receiver in conventional broadcast receivers, it is not entirely satisfactory in receivers operating at the higher frequencies. The problems of maintaining satisfactory operation of a receiver at high frequency,

of say around 1290 megacycles, becomes increasingly difficult as the frequency increases, until there comes a point where conventional wiring, as in low frequency receivers, will not provide an operative high frequency receiver. This is true in connection with the provision of a ground separat from the chassis in A. C.-D. C. high frequency receivers. The length of the ground leads is such that they add such inductance to the circuits that they cannot, without special precautions, be made to tune to the desired frequency.

Therefore, it is desirable to have the receiver chassis act as the ground for the various circuits of a receiver since it enables a simpler and considerably cheaper construction to be effected as well as enabling a more stable operation.

It is, therefore, desirable to provide a housing for the chassis such that unauthorized persons cannot accidentally or even purposely obtain contact therewith, without going to considerable trouble.

Heretofore this has been effected by providing insulated shafts which extend through the cabinet. This is not only expensive construction but is also undesirable since a composite shaft is apt to become loose or break and render the control inoperative.

By my present invention, I have provided an improved control wherein the chassis and its component parts may be made in a conventional manner. Briefly, this is effected by providing composite control knob for the standard shafts, one portion of which is applied to the shaft before the chassis is placed in the cabinet, and the other part of which is applied to the first part after the chassis is installed in the cabinet. With such a control, even if the last applied knob should become loose and fall oif, the other portion still remains on the shaft and cannot be removed without taking the chassis out of the cabinet.

Still further advantage resides in the provision of means which will prevent the insertion of slender metallic objects into the cabinet even after the outer knob is removed. This is particularly desirable since in production of radio receivers, it is customary to make the apertures through which the control extends, larger than the shaft which is to go therethrough, to assure that the shaft will not bind in the hole, and that no difiiculties will be encountered in assembly of the receiver chassis in the cabinet due to misalignment of the receiver controls with the cabinet apertures.

Other advantages of the invention, and. the invention itself, will be apparent from the following specifications when considered in conjunction with the accompanying drawing in which:

Fig. 1 is a vertical section to illustrate an application of the invention in conjunction with a 3 radio receiving set having a chassis, a portion of which is broken away to reveal an instrument in association therewith; and

Fig. 2 is a vertical section taken on line 22 of Fig. 1.

In the drawing, the reference character 3 is used to denote the cabinet of a radio receiving set which may be of plastic, wood or other composition. A metal chassis 4 is disposed inside and supported by the cabinet. As one of several possible instruments for controlling the receiver, a volume control I5 is illustrated adapted to be carried by a vertical wall I of the chassis i. The volume control 6 has a threaded sleeve 8 by means of which, and a nut 9, it is secured to the wall I. Axially of the sleeve 8 a metal control shaft II extends from the volume control 6 for use in the usual manner.

Means by which the shaft II is adapted to be rotated from the exterior of the cabinet includes an insulating member or cap I2 which may extend through an aperture or hole I3 in a wall of the cabinet 3. The cap is of such a structure that it completely insulates the shaft I i from the exterior of the cabinet; that is, from members outwardly of the cabinet such as the hand of an operator to which an electric current could be communicated by the shaft were the insulation member I2 not employed. Although a cap I2 of molded Bakelite having a, bore I5 of limited 5 depth to receive shaft I I is a preferred construction, I also contemplate use of a tubular section of any effective insulating material, one end of which is adapted to be plugged with an insulating agent to electrically segregate the extremity of the shaft from the exterior of the cabinet.

A safety precaution against tampering with elements of the radio receiver, within the cabinet, is also provided. This precaution is particularly intended as a safety measure for an unauthorized individual, such as a child, who might be inclined to insert a wire or rod-like conductive member into the space between the cap I2 and the interior of the aperture I3. Therefore, that end of the cap I2 which is within the cabinet is provided with a guard or stop in the form of a flange I4, of diameter substantially greater than the diameter of the aperture. This difference in diameters is advisable since the flange I4 must cover the aperture I3, even if the axis of the cap I2 is in spaced relationship to the axis of the aperture. Although the flange may take the form of any element disposed in substantially perpendicular relationship to the axis of the cap I2, and insulated from shaft I I, I prefer to employ a cap with which the flange I4 is an integral part, for the sake of convenience of manufacture.

Any convenient means may be employed for attaching the cap I2 to the shaft I I. A desirable manner in which the shaft II is adapted to be drivingly associated with the cap I2 is to provide the shaft I! with a straight-knurled surface and by means of a slot it which splits the end portion of the shaft thereby providing an operative connection between the two parts. Although the cap I2 is thus adapted to he slid on and off the shaft II, prior to installation of the chassis i in the cabinet 3, the flange It provides for positively locking the capin operative relationship with the shaft and the cabinet once the chassis is installed in the cabinet. Furthermore, owing to the increased diameter of the flange relative to the diameter of the cap, in extension through the aperture I3, the likelihood of splitting the cap,

as the shaft I I is initially forced into it, is greatly reduced or completedly obviated.

Although the operation of the volume control 6 may be varied by grasping the cap I2 to turn shaft ii, I prefer to employ a suitable control member or knob II for operating the volume control. A convenient means of attaching the knob H to the cap I2 is to provide in the knob a socket c in which the end of the cap is received and where it is clamped by a set screw I9.

Having thus described my invention in an embodiment thereof, I am aware that numerous and extensive departures may be made therefrom without departing from the spirit or scope of the appended claims.

I claim:

1. In a radio receiving set which includes a substantially closed cabinet having an aperture in a wall thereof and within the cabinet a chassis bearing an instrument having a shaft for adjustment of the instrument which shaft is adapted to extend toward the aperture, in combination, an insulation member carried by said shaft and extending through said aperture, said member having a diameter interiorly of the cabinet greater than the diameter exteriorly of the cabinet to anchor said member to said cabinet, the portion of said insulation extending exterior'ly of said cabinet being adapted to receive a control member in driving relationship thereto,

ans including said insulation member whereb said shaft is completely insulated from the exterior of the cabinet, means by which the insulating member is adapted to be drivingly associated with said shaft, and means providing for variablypositioning said insulating member axially of said shaft and in driving relationship thereto.

2. In a radio receiving set which includes a substantially closed cabinet and means providin a circular hole in a wall thereof and within the cabinet a chassis bearing .an instrument having a shaft for adjustment of the instrument, which shaft is adapted to extend toward the aperture, in combination, a cap carried by said shaft in extension through said aperture and adapted to support a manual control member at one end thereof, a flange formed integrally with the other end of said member, said flange and cabinet providing a substantial closure for said chassis when the axis of said shaft is spaced from the axis of said hole thereby providing an obstacle for passage of a conductor through said hole.

3. In a radio receiving set which includes a substantially closed cabinet having an aperture in a wall thereof and within the cabinet a chassis bearing an instrument having a shaft for adjustment of the instrument which shaft is adapted to extend toward the aperture, in combination, an insulation member of uniform diameter extending through said aperture the portion of said member extending through said aperture being hollow and adapted to provide frictional driving relationship with said shaft, the portion of said member in extension outwardly of the cabinet being solid and providing means by which turning motion is adapted to be communicated to said shaft, and a flange formed in-- tegrally on said hollow end to resist splitting of said member when associated with said shaft, said flange also being adapted to exclude passage of conductor members through said aperture.

l. In a radio receiving apparatus of the class described comprising a substantially closed cabinet, a circular aperture in a wall thereof and within the cabinet a current-carrying chassis bearing a control instrument, and a removable control knob for the exterior of the cabinet, means by which rotation of the knob is adapted to be communicated to said instrument comprising, an adjustment shaft extending from said instrument toward said aperture, said shaft being in electrical communication with said chassis, an insulating member in telescopic relationship to said shaft and to said knob and extending through said aperture, said member being axially adjustable on said shaft and a flange on said insulating member inside the cabinet to prevent passage of a wire-like member into the cabinet by way of said aperture, the edge of said flange being adapted to overlie the edge of the aperture regardless of the relationship of the axis of said insulation member relative to the axis of said aperture.

5. In a radio receiving apparatus of the class described comprising a substantially closed cabinet, a circular aperture in a wall thereof and within the cabinet a chassis bearing a volume control instrument and a removable control knob for the exterior of the cabinet, means by which rotation of the knob is adapted to be communi- CLIFFORD F. HOFFMAN.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 756,979 Perkins Apr. 12, 1904 1,595,863 Driggs, Jr. Aug. 10, 1926 1,639,885 Gammeter Aug. 23, 1927 2,147,140 Blain Feb. 14, 1939 FOREIGN PATENTS Number Country Date 383,461 Great Britain, Nov. 17, 1932 567,934 Germany Dec. 22, 1932 

